Polyimide films are known to have excellent electrical insulating properties, as well as high mechanical strength and resistance to chemical degradation. Such films are often used as a base film for flexible circuit boards laminated to metal foils, such as copper foil or the like. However, unwanted static build-up and discharge can occur with standard polyimide films, and this can be problematic in certain types of circuit design. A need therefore exists for a polyimide film having anti-static properties without unduly harming other desired polyimide properties, e.g., high heat resistance, thin layer formability, high mechanical flexibility and excellent toughness.
U.S. Pat. No. 5,078,936 discloses an electrically conductive polyimide film with a carbon powder filler. Surface resistivity of these films range from about 130 ohms/square to 1010 ohms/square depending on the loading level of carbon used.